Why Are Our Brains So Big? Scientists Have a Few Possible Answers

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iStock

Human brains are big. They account for about 2 percent of our body mass—a higher percentage than most other species—and they’re triple the size of those belonging to our common ancestor, the ape-like Australopithecines. While there’s no consensus on how and why our brains got to be so big, scientists have suggested a new theory that contradicts earlier ideas.

As phys.org reports, a study published in the journal Nature contains evidence that the human brain evolved in response to ecological stress. Faced with a harsh environment, the brain grew to help humans better survive and provide for their offspring, the scientists believe. Previously, studies suggested that the brain evolved as humans began to engage in more complex social interactions. The researchers behind this new study say their findings suggest otherwise.

“The findings are intriguing because they suggest that some aspects of social complexity are more likely to be consequences rather than causes of our large brain size,” Mauricio González-Forero, the paper’s co-author and a mathematical evolutionary biologist at Scotland’s University of St. Andrews, tells phys.org. “The large human brain is more likely to stem from ecological problem-solving and cumulative culture than it is from social maneuvering.”

They reached this conclusion by using computer software to simulate evolution. Data relating to how much energy an adult human female needs to support the brain was plugged in, as well as energy requirements relative to body size, the Indiana Gazette reports.

Overall, researchers determined through their model that the main challenges that spurred brain growth were overwhelmingly (60 percent) ecological in nature, but it also may have resulted from cooperation (30 percent) and competition between groups (10 percent). Researchers said the ability to acquire new skills is also a crucial component when considering how human brains evolved.

“Ecological challenges can only lead to brain size of this scale if they are coupled with the ability to continue learning from others,” González-Forero said. “The paper is suggesting that human brain development is an interaction between these two things—ecological pressures and culture.”

[h/t phys.org]

Why Is Pee Yellow?

Chloe Effron
Chloe Effron

WHY? is our attempt to answer all the questions every little kid asks. Do you have a question? Send it to why@mentalfloss.com.

Your body is kind of like a house. You bring things into your body by eating, drinking, and breathing. But just like the things we bring home to real houses, we don’t need every part of what we take in. So there are leftovers, or garbage. And if you let garbage sit around in your house or your body for too long, it gets gross and can make you sick. Your body takes out the garbage by peeing and pooping. These two things are part of your body’s excretory system (ECKS-krih-tore-eee SISS-tem), which is just a fancy way of saying “trash removal.” If your body is healthy, when you look in the toilet you should see brown poop and yellow pee.

Clear, light yellow pee is a sign that your excretory system and the rest of your body are working right. If your pee, or urine (YER-inn), is not see-through, that might mean you are sick. Dark yellow urine usually means that you aren’t drinking enough water. On the other hand, really pale or colorless pee can mean you might be drinking too much water! 

Your blood is filtered through two small organs called kidneys (KID-knees). Remember the garbage we talked about earlier? The chemicals called toxins (TOCK-sins) are like garbage in your blood. Your kidneys act like a net, catching the toxins and other leftovers and turning them into pee.

One part of your blood is called hemoglobin (HEE-moh-gloh-bin). This is what makes your blood red. Hemoglobin goes through a lot of changes as it passes through your body. When it reaches your kidneys, it turns yellow thanks to a chemical called urobilin (yer-ah-BY-lin). Urobilin is kind of like food coloring. The more water you add, the lighter it will be. That's why, if you see dark yellow pee in the toilet, it's time to ask your mom or dad for a cup of water. 

To learn more about pee, check out this article from Kids Health. 

Why Do Grown-Ups Have Wrinkles?

Chloe Effron / iStock
Chloe Effron / iStock

WHY? is our attempt to answer all the questions every little kid asks. Do you have a question? Send it to why@mentalfloss.com.

Our skin is supposed to stretch. We do it every day when we squint in the sunlight, make a silly face, smile, laugh, pout, or furrow our eyebrows. Each time our skin stretches, tiny lines and grooves start to form below the surface. Over time, the outside skin gets thinner and dryer, and it falls deeper into those little grooves. As we get older, we also lose some of the stuff in our skin that helps it to stretch and then return to its normal place. 

First, let’s talk about our three layers of skin. The outside part is called the epidermis (eh-pih-DER-mis). That’s the part you can see. Under that is our dermis, where we have stretchy fibers called elastin that let our skin stretch and then go back to its normal position, just like an elastic hair band. The dermis layer also has collagen (KAHL-uh-jen), a protein that helps it stay sturdy and grow new skin cells. Under the dermis is the deep subcutaneous (sub-kyoo-TAY-nee-us) layer, which stores fat. As we get older, we start to lose collagen, elastin, fat, and oils made by our skin that keep it moisturized, or less dry.

There are lots of reasons. Our bodies make less of these things as we age, so our skin gets thinner, drier, and less stretchy. The Sun’s ultraviolet (UV) light also breaks down collagen and elastin fibers. This causes more lines and wrinkles. But wrinkles are just a part of life. One day, you’ll have them too. Take good care of your skin by wearing sunscreen and drinking plenty of water to help your skin stay moisturized.

For further reading, visit Kids Health.


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